Diagnosis of soft tissue tumors using immunohistochemistry as a surrogate for recurrent fusion oncoproteins

Nuclear DUX4 immunohistochemistry is a highly sensitive and specific marker for the presence of CIC::DUX4 fusion in CIC-rearranged sarcomas: a study of 48 molecularly confirmed cases

AIMS

CIC-rearranged sarcomas (CRS) are clinically aggressive undifferentiated round cell sarcomas (URCS), commonly driven by CIC::DUX4. Due to the repetitive nature of DUX4 and the variability of the fusion breakpoints, CIC::DUX4 fusion may be missed by molecular testing. Immunohistochemical (IHC) stains have been studied as surrogates for the CIC::DUX4 fusion. We aim to assess the performance of DUX4 IHC in the work-up of CRS and its expression in non-CRS round cell or epithelioid neoplasms.

METHODS AND RESULTS

Cases of molecularly confirmed CRS (n = 48) and non-CRS (n = 105) were included. CRS cases consisted of 35 females and 13 males, with ages ranging from less than 1 year to 67 years (median = 41 years). Among the molecularly confirmed non-CRS cases, C-terminal DUX4 expression was investigated in Ewing sarcomas (38 cases), alveolar rhabdomyosarcomas (18 cases), desmoplastic small round cell tumours (12 cases) and synovial sarcomas (n = five), as well as in non-mesenchymal neoplasms such as SMARCA4/SMARCB1-deficient tumours (n = five), carcinomas of unknown primary (n = three) and haematolymphoid neoplasms (four cases). DUX4 IHC was considered positive when strong nuclear expression was detected in more than 50% of neoplastic cells. When used as a surrogate for the diagnosis of CRS, the sensitivity and specificity of DUX4 IHC was 98 and 100%, respectively. Only one CRS case was negative for DUX4 IHC and harboured a CIC::FOXO4 fusion.

CONCLUSIONS

DUX4 IHC is a highly sensitive and specific surrogate marker for the presence of CIC::DUX4 fusion, demonstrating its utility in establishing a diagnosis of CRS.

Steady survival improvements in soft tissue and bone sarcoma in the Nordic countries through 50 years

PURPOSE

Sarcomas are rare cancers with many subtypes in soft tissues, bone and cartilage. International survival trends in these cancers are not well known. We present 50-year survival trends for soft tissue sarcoma (STS) and bone sarcoma (BS) in Denmark (DK), Finland (FI), Norway (NO) and Sweden (SE).

METHODS

Relative 1-, 5/1 conditional- and 5-year survival data were obtained from the NORDCAN database for years 1971-20. We additionally estimated annual changes in survival rates and determined significant break points.

RESULTS

In the last period, 2016-20, 5-year survival in STS was best for NO men (74.6%) and FI women (71.1%). For the rarer BS, survival rates for SE men (72.0%) and DK women (71.1%) were best. Survival in BS was lower than that in STS in 1971-75 and the difference remained in 2016-20 for men, but for women the rates were almost equal. Sex- and country-specific differences in survival in STS were small. The 50-year improvement in 5-year survival in STS was highest in NO men, 34.0 % units and FI women, 30.0 % units. The highest improvements in BS were in SE men 26.2 % units and in FI women 29.2 % units.

CONCLUSIONS

The steady development in survival over the half century suggests contribution by stepwise improvements in diagnostics, treatment and care. The 10-15% mortality in the first year probably indicates diagnostic delays which could be improved by organizing patient pathways for aggressive rare diseases. Early diagnosis would also reduce metastatic disease and breakthroughs in treatment are a current challenge.

CHRNA6 RNA In Situ Hybridization Is a Useful Tool for the Diagnosis of Extraskeletal Myxoid Chondrosarcoma

Extraskeletal myxoid chondrosarcoma (EMC) is an uncommon mesenchymal neoplasm characteristically composed of uniform-appearing round to spindle-shaped cells with eosinophilic cytoplasm and abundant myxoid extracellular matrix. Although the majority of cases harbor a pathognomonic t(9;22) translocation that fuses EWSR1 with the orphan nuclear receptor NR4A3, there are less common variants that partner NR4A3 with TAF15, TCF12, or TFG. By immunohistochemistry, EMC has features of both cartilaginous and neuroendocrine differentiation, as evidenced by inconsistent expression of S100 protein and synaptophysin or INSM1, respectively, in a subset of cases. Given the limitations of available immunohistochemical stains for the diagnosis of EMC, we analyzed genome-wide gene expression microarray data to identify candidate biomarkers based on differential expression in EMC in comparison with other mesenchymal neoplasms. This analysis pointed to CHRNA6 as the gene with the highest relative expression in EMC (96-fold; P = 8.2 × 10-26) and the only gene with >50-fold increased expression in EMC compared with other tumors. Using RNA chromogenic in situ hybridization, we observed strong and diffuse expression of CHRNA6 in 25 cases of EMC, including both EWSR1-rearranged and TAF15-rearranged variants. All examined cases of histologic mimics were negative for CHRNA6 overexpression; however, limited CHRNA6 expression, not reaching a threshold of >5 puncta or 1 aggregate of chromogen in >25% of cells, was observed in 69 of 685 mimics (10.1%), spanning an array of mesenchymal tumors. Taken together, these findings suggest that, with careful interpretation and the use of appropriate thresholds, CHRNA6 RNA chromogenic in situ hybridization is a potentially useful ancillary histologic tool for the diagnosis of EMC.

Current Approach to Undifferentiated Neoplasms, With Focus on New Developments and Novel Immunohistochemical Stains

CONTEXT.—

Workup of the poorly differentiated or undifferentiated tumor remains a significant and challenging entity in the practice of anatomic pathology. Particularly in the setting of small biopsies and limited material, these cases demand a balanced approach that considers the patient's clinical and radiologic presentation, a basic assessment of tumor morphology, a reasonably broad immunohistochemical panel, and diligent preservation of tissue for prognostic and therapeutic studies.

OBJECTIVE.—

To illustrate some of the new and emerging immunohistochemical markers in the evaluation of tumors with undifferentiated or poorly differentiated morphology, with a focus on the workup in limited tissue samples to raise awareness of the issues involved with the pathologic workup in these challenging tumors.

DATA SOURCES.—

A literature review of new ancillary studies that can be applied to cytologic specimens was performed.

CONCLUSIONS.—

Knowledge of the patient's history and communication with the patient's clinical team is essential in formulating a differential diagnosis that can appropriately limit the differential diagnosis based on morphology, especially in small specimens. This information, in conjunction with classifying the tumor morphology (eg, epithelioid, spindled, neuroendocrine, basaloid/biphasic, mixed) gives a logical approach to choosing an initial immunohistochemical panel. Fortunately, immunohistochemistry is evolving quickly in the wake of groundbreaking molecular studies to develop new and better markers to further classify these difficult tumors beyond where we traditionally have been able to go.

Diagnostic utility of FOXO1 immunohistochemistry for rhabdomyosarcoma classification

AIMS

Rhabdomyosarcomas currently are classified into one of four subtypes (alveolar, embryonal, spindle cell/sclerosing, or pleomorphic) according to their morphological, immunohistochemical, and molecular genetic features. The alveolar subtype is characterised by a recurrent translocation involving PAX3 or PAX7 and FOXO1; identification of this translocation is important for appropriate classification and prognostication. In this study, we aimed to explore the diagnostic utility of FOXO1 immunohistochemistry for rhabdomyosarcoma classification.

METHODS/RESULTS

A monoclonal antibody targeting a FOXO1 epitope retained in the fusion oncoprotein was used to study 105 rhabdomyosarcomas. FOXO1 was positive for expression by immunohistochemistry in all 25 alveolar rhabdomyosarcomas, with 84% showing diffuse expression in greater than 90% of neoplastic cells; the remainder of alveolar rhabdomyosarcomas displayed at least moderate staining in a minimum of 60% of lesional cells. Apart from three spindle cell rhabdomyosarcomas showing heterogeneous nuclear immunoreactivity in 40-80% of tumour cells, the 80 cases of embryonal, pleomorphic, and spindle cell/sclerosing rhabdomyosarcoma were negative for FOXO1 expression (96.3% specific) when using a threshold of nuclear staining in 20% of neoplastic cells to determine positivity. Variable cytoplasmic staining was present in a fraction of all rhabdomyosarcoma subtypes. Nonneoplastic lymphocytes, endothelial cells, and Schwann cells also showed variably intense nuclear anti-FOXO1 immunoreactivity.

CONCLUSION

Taken together, our findings suggest that FOXO1 immunohistochemistry is a highly sensitive and relatively specific surrogate marker of the PAX3/7::FOXO1 fusion oncoprotein in rhabdomyosarcoma. Cytoplasmic immunoreactivity, expression in nonneoplastic tissues, and limited nuclear staining of nonalveolar rhabdomyosarcomas represent potential pitfalls in interpretation.

A Rare Case of Primary Epithelioid Hemangioma of Bone with WWTR1::FOSB Fusion: A Benign Lesion with the Potential to Mimic Malignancy

Epithelioid hemangioma of bone is a rare benign, locally aggressive vascular tumor that can be particularly challenging to diagnose given its frequent multifocality, non-specific imaging findings, and wide range of morphologic appearances. Additionally, some epithelioid hemangiomas demonstrate atypical histologic features including increased cellularity, necrosis, and moderate cytologic atypia - characteristics that may raise concern for malignancy. Molecular studies can serve as a powerful, objective tool in the differential diagnosis of diagnostically challenging epithelioid vascular tumors. Importantly, FOS and FOSB gene rearrangements have been identified as the genetic hallmarks of osseous epithelioid hemangioma, present in greater than 70% of cases. FOSB-fusion-positive epithelioid hemangioma, in particular, may display atypical histologic features. While ZFP36 is the typical FOSB fusion partner in epithelioid hemangioma, we herein present a case of epithelioid hemangioma of bone with a rare WWTR1::FOSB fusion. This case demonstrates the diagnostic challenges associated with epithelioid hemangioma, especially in the setting of FOSB gene rearrangements, and the importance of genomic studies in the work up of these vascular tumors.